1. Field of the Invention
The present invention relates to a stereoscopic optical element. More specifically, the present invention relates to an optical element having birefringent photosensitive films arranged on a plurality of regions and having mutually different slow axes or fast axes, and an image display device capable of providing a two-dimensional or three-dimensional display using the optical element.
2. Description of the Background Art
Conventionally, an optical element such as a retarder film has been fabricated by uniaxial rolling of a polymer film. Therefore, in the optical element such as the retarder film fabricated in this manner, the direction of slow axes or fast axes is uniform throughout the plane. Inventors including inventors of the present invention proposed a birefringent new photosensitive film in U.S. Ser. No. 08/702,763 (corresponding to Japanese Patent Laying-Open No. 9-068699). In this copending application, the photosensitive film is used in a liquid crystal display having an optically isotropic polymer region such as a polymer wall and a liquid crystal region filled with liquid crystal in a liquid crystal display panel, as an optical element for independent color compensation of the liquid crystal region and the polymer region, utilizing the retarder film.
There is a long history of various attempts to reproduce a three-dimensional image or a stereoscopic image. Various and many attempts including a laser hologram and the like have been known. However, only the following three methods can be named as highly complete methods of stereoscopic image display, capable of displaying motion pictures in full color using three primary colors. In these methods, images for the right eye and the images for the left eye are provided separate from each other, based on the principle that the viewer feels the field of depth because of binocular parallax, that is, offset between the images for the left and right eyes.
(1) The first method is Field Sequential Shuttered Glasses Stereoscopic, in which images for the left and right eyes are displayed alternately in time-divisional manner by one display device. Glasses having electric shutter function are alternately opened/closed in synchronization with the displayed image, thereby realizing stereoscopic image display. This method is. applicable both to projection display and direct view display.
(2) The second method is Autostereoscopic Imaging. In this method, striped images for both left and right eyes in lengthwise or widthwise direction displayed on an image display device are allotted to the left and right eyes by a lenticular sheet or a slitted plate in the lengthwise or widthwise direction placed in front of the display device. In this manner, this method allows viewing a stereoscopic image without mounting any specific binocular or eyeglasses.
(3) The third method is Polarizing Binocular Stereoscopic Imaging. In this method, images for the left and right eyes are linearly polarized with directions of polarization forming an angle of 90.degree. with each other, and the images are observed by a polarizing binocular, thus enabling stereoscopic image display. For projection display, two polarizing projectors are used and two images are overlapped on a screen. For direct view display, images of two display devices are synthesized by a half mirror or a polarizing mirror.
The first method mentioned above is advantageous in that stereoscopic image display is possible by only one display device. However it is disadvantageous in that the viewer must wear a binocular or eyeglasses having electric shutter function (for example, liquid crystal shutter eyeglasses). Such eyeglasses are heavy, unavoidably causing fatigue of the viewer when used for a long period of time. In addition, such eyeglasses with shutter function are expensive. Since one viewer needs one binocular, the cost for purchasing the necessary number of binoculars corresponding to the number of viewers would be formidable.
The stereoscopic image obtained by the second method is advantageous that the image can be observed without the necessity for the viewer to wear a special binocular or the like. However, Autostereoscopic Imaging is disadvantageous in that a zone allowing stereoscopic imaging is very narrow. The reason will be described with reference to an example employing a lenticular lens.
Referring to FIG. 9, which is a plan view of a display device 900 and a viewer 907 viewed from above, a zone Y1r allowing stereoscopic view in left/right direction will be described. Display device 900 has an arrangement of a plurality of components 901 including pixels for right eye 901(r) and pixels for left eye 901(l), with a black matrix 902 provided between each of the components 901. On an entire surface of display device 900, a lenticular sheet 905 having cylindrical lenses 906 at a pitch of left and right two components, is adhered by an adhesive 904. Images are allotted to the left and right eyes of viewer 907 by lenticular sheet 905.
At this time, when the left eye of viewer 907 is positioned in the range between C-D of FIG. 9 and the right eye of viewer 907 is positioned in the range between E-F, a normal stereoscopic image is observed by viewer 907. However, when both eyes of viewer 907 move and one of the eyes is positioned in the range between D-E, for example, that eye sees the non-display portion responding to the black matrix 902, and hence a stereoscopic image cannot be observed. The same applies when one of the eyes is positioned between B-C or F-G. Further, when the left eye is positioned between E-F and the right eye is positioned between G-H, the left and right images are inverted, and a normal stereoscopic image cannot be observed. Therefore, in the second method, in principle, the width of one zone allowing stereoscopic view cannot exceed the space between both eyes of the viewer.
Further, when both eyes of the viewer move exceeding that range in which left and right images are inverted, a region (side lobe) where a normal image is again observed appears. In this Autostereoscopic Imaging, it may possible for a few viewers to observe stereoscopic images by positively utilizing the side lobes. However, the zone allowing stereoscopic view of each side lobe is also very narrow.
A zone allowing stereoscopic view in the forward/rearward direction will be described with reference to FIGS. 9 and 10. In FIG. 10, portions corresponding to those of FIG. 9 are denoted by the same reference characters. Referring to FIG. 9, assume that light beams 1, 2, . . . , 7, 8 are emitted from display components in which left and right two components constitute a set, from opposing ends and the center of display device 900. At this time, the zone allowing stereoscopic view in the forward/rearward and left/right directions is represented by hatched portions in FIG. 10. Here, the space between both eyes of viewer 907 will be represented by e, lateral length of display device 900 by Hh, and a distance at which widest zone allowing stereoscopic view in the left/right direction is obtained (optimal distance for stereoscope) by L (when a stereoscopic image is viewed from a position at a distance L, the zone allowing stereoscopic view in left/right direction becomes the widest). Distances by which viewer 907 can move in the forward and rearward directions from the optimal distance L for stereoscope can be represented by the following equations (1) and (2), in accordance with expressions described in "Autostereoscopic 3-D Television Using Eight TV Cameras" (H. Isono et al., NHK Technical Laboratory R&D, November, 1995, pp. 43-54).
Zone allowing stereoscopic view in forward direction EQU Yf=e.times.L/(Hh+2.times.e) (1)
Zone allowing stereoscopic view in rearward direction EQU Yb=e.times.L/Hh (2)
Assume that a TFT liquid crystal display panel having a 10.4 inch diagonal (length H=156 mm, width Hh=208 mm) is used as display device 900. When we assume that the space between both eyes of the viewer is 65 mm and the observing distance L=350 mm, the distance by which the viewer can move forward or rearward would be Yf=67 mm and Yb=109 mm from equations (1) and (2). When the viewer moves forward or rearward exceeding this scope, stereoscopic image cannot be observed.
Further, there is a problem that stereoscope obtained by the side lobe is inferior in quality. Japanese Patent Laying-Open No. 4-16092 discloses a method of removing a side lobe by using a light-blocking plate, in order to solve this problem.
The concept of the method disclosed in this laid-open application will be described with reference to FIG. 11. Referring to FIG. 11, in this method, in front of a lenticular sheet 802 having cylindrical lenses arranged periodically in a horizontal direction of a display screen 802, a light-blocking plate 803 for limiting a viewing angle in the horizontal direction of the display screen is arranged. Each cylindrical lens extends parallel to a direction vertical to the display screen. Light-blocking plate 803 has a light-shielding layer 804 provided along the direction vertical to the display screen, and removes the side lobe by blocking light beam from components other than the proper left and right components. In this method, stereoscopic observation utilizing only the main lobe with high image quality is realized.
Further, Japanese Patent Laying-Open No. 6-335030 discloses a stereoscopic image display device provided with a mask for changing optical path of light beams, corresponding to non-transmitting portion between the lenticular sheet and the display device. The concept is as shown in FIG. 12. Referring to FIG. 12, a diffusion plate 706 having a diffusion layer 702 is arranged in front of a region of a non-displaying portion 705 (black matrix) existing between a pixel for left eye and a pixel for right eye. Diffusion plate 706 diffuses light beams from portions other than the non-displaying portion, thus a stereoscopic image is obtained while suppressing generation of a black fringe.
Finally, the third method includes a method which allows observation of a two-dimensional image normally and allows observation of a stereoscopic image by mounting a polarizing binocular. In this method, for projection display, two polarizing projectors are used and two images are overlapped on the screen, for forming a stereoscopic image. For direct view display, images from two display devices are synthesized by a half mirror or a polarizing mirror, or polarizing transmission axes of polarizing film arranged on a substrate surface are made different component by component, whereby images with different states of polarization are formed for the right eye and the left eye.
The stereoscopic image thus obtained is free of any flickers, and the viewer can observe the stereoscopic image by wearing a very light and inexpensive polarizing binocular. However, in order to provide two images with different polarization axes simultaneously without fail, two display devices or two projectors are necessary. Accordingly, the system is too expensive for family use.
Another example of the third method is disclosed in Japanese Patent Laying-Open No. 58-184929. In this method, mosaicwise polarizing layer in which polarization axes cross orthogonal to each other between adjacent components is tightly adhered on a front surface of one display device, and a viewer can observe a stereoscopic image by wearing a polarizing binocular.
In this method, referring to FIG. 13, on a front surface of a glass layer 604 providing a face plate, such as a CRT on which pixels for right eye 607 and pixels for left eye 605 are allotted, polarizing plates 602a and 602b having mutually orthogonally intersecting polarization axes are arranged. Polarizing layers 602a and 602b are patterned mosaicwise with the size of each mosaic being at a pixel level, such that polarizing transmission axes of adjacent components intersect orthogonal to each other. Since polarization layers 602a and 602b are patterned in the order of micrometer in accordance with the size of the pixel level, such polarization layers will be hereinafter referred to as micropolarization plate. It is possible for the viewer to observe a stereoscopic image when the viewer observes images displayed on the CRT or the like through polarization binocular 603 provided with polarization plates 603a and 603b of which left and right polarization axes intersect orthogonally with each other. Therefore, a large number of viewers may observe stereoscopic images by wearing the polarization binoculars.
Japanese Patent Laying-Open No. 62-135810 discloses a display device capable of stereoscopic image display using a single display device, by providing a polarization layer having partially different polarization directions, inside a glass substrate constituting a liquid crystal display device. The concept is as shown in FIG. 14. A liquid crystal display device includes a liquid crystal layer 505 sealed in a region between a pair of glass substrates 501a and 501b, with its periphery sealed by a seal 506. Glass substrates 501a and 501b are provided with interconnection layers 503a and 503b for applying a voltage to liquid crystal layer 505, and alignment films 504a and 504b for aligning liquid crystal molecules of liquid crystal layer 505, respectively. As can be seen from FIG. 14, polarization layers 502a and 502b having partially different polarization directions are provided between interconnection layers 503a, 503b and glass substrates 501a, 501b, respectively.
Further, U.S. Pat. No. 5,537,144 discloses a stereoscopic display device in which a liquid crystal panel and a micropolarization plate fabricated by patterning a rolled polyvinylalcohol layer using a resist material are combined. Referring to FIG. 18, according to U.S. Pat. No. 5,537,144, a micropolarization plate 302 is superposed on an SMI (Spatially Multiplexed Image) 301 displaying in complexed manner, images for the right eye and for the left eye, and the viewer observes wearing polarization binocular 603 provided with polarization plates 603a and 603b of which left and right polarization axes intersect orthogonally with each other, whereby a stereoscopic display is obtained.
In Autostereoscopic Imaging described as the second method, the width in the left/right direction of the zone allowing stereoscopic imaging is limited to a very narrow range as shown in FIGS. 9 and 10, and the zone is also limited in the forward/rearward direction. Further, in this method, two components arranged in the direction of signal lines (horizontal direction on the screen) are used as one set for stereoscopic display. For this reason, the zone allowing stereoscopic imaging is further narrowed because of a non-displaying portion (black matrix) existing between the two components.
In the image display device disclosed in Japanese Patent Laying-Open No. 4-16092 shown in FIG. 11 and Japanese Patent Laying-Open No. 6-335030 shown in FIG. 12, it is possible to provide stereoscopic image display resulting from main lobe only with high quality, or stereoscopic image display with generation of the black fringe derived from the presence of the non-displaying portion suppressed, as described above. However, means for allotting the left and right images to both eyes of the viewer is the lenticular sheet. The lenticular sheet employs a plurality of cylindrical lenses arranged to correspond to a total of two components, that is, one for the left eye and one for the right eye, arranged in the horizontal direction on the display screen. Therefore, when a two-dimensional image is observed by such an image display device, the horizontal resolution of the two-dimensional image is degraded to 1/2 of the original horizontal resolution of the display device. When the components for the left eye and for the right eye are arranged alternately in the horizontal direction, it is necessary to switch and supply to the display device image signals for the left eye and image signals for the right eye alternately at an exact timing, with the period corresponding to 1H period/(number of components in the horizontal direction). This requires a complicated display circuit. Further, in the case of the device disclosed in Japanese Patent Laying-Open No. 4-16092 shown in FIG. 11, stereoscopic image observation by a number of viewers is difficult, as the side lobes are removed.
When a stereoscopic image is to be observed by the display device disclosed in Japanese Patent Laying-Open No. 58-184929 shown in FIG. 13, it is necessary that polarizing transmission axes of polarizing plate 602a for the right eye arranged on the component 607 for the right eye and of the polarizing plate 602b for the left eye arranged for the component 605 for the left eye of a CRT or the like are exactly matched with polarizing transmission axes of polarizing plates 603a and 603b for the right and left eyes of the polarizing binocular which the viewer wears. When the axes are in exact matching, a stereoscopic image is observed. However, when the axes do not exactly match, as in the case when the viewer moves upward or downward, images for the right eye and for the left eye are mixed and observed by both eyes (cross talk), and thus stereoscope fails.
Here, the size Yud of a zone allowing stereoscopic view in which the viewer can move upward (a direction parallel to the lengthwise direction of the image screen) while observing a stereoscopic image normally in FIG. 13 is represented by the following equation (3). Here, P represents pitch of the display components, B represents width of a non-displaying portion (black matrix), L represents distance from the viewer to the display device, and d represents thickness of the glass layer in air. EQU Yud=B.times.L/d (3)
For example, assume that a TFT liquid crystal display panel with 10.4 inch diagonal is used in place of a CRT, as a device for displaying images for the right eye and for the left eye in FIG. 13. It is assumed that the pitch P of one display component of TFT liquid crystal display panel is 0.33 mm, and the width B of the non displaying portion is 0.03 mm. A counter substrate of liquid crystal display panel corresponds to glass plate 604 as the face plate shown in FIG. 13. When thickness d1 of the counter substrate is assumed to be 1.1 mm and refractive index of the substrate is assumed to be 1.52, thickness d of counter substrate in air is 0.72 mm. Therefore, when the distance L from the viewer is 350 mm, the size of the zone allowing stereoscopic view and allowing movement in upward/downward direction is, according to the equation (3), Yud=14.5 mm. In other words, the viewer may move only by 7 mm in upward or downward direction from the center of the screen, and when this distance is exceeded, cross talk occurs.
U.S. Ser. No. 08/702,763 (Japanese Patent Laying-Open No. 9-068699) commonly owned by the applicant of the present application discloses a technique in which a retardation value is selectively set to a desired amount at an arbitrary position. The retardation value at other portions may be any value.
In Japanese Patent Laying-Open No. 62-135810 shown in FIG. 14, polarization layers 502a and 502b having partially different polarization directions are arranged inside the liquid crystal display panel so as to prevent generation of cross talk between left and right images. Here, polarization layers 502a and 502b are fabricated by a uniaxially rolled polyvinylalcohol. After polarization layers 502a and 502b are formed on the substrate, interconnection layers 503a and 503b as well as alignment films 504a and 504b are formed. However, heat resistance of polyvinylalcohol is not sufficient considering the process steps for manufacturing a liquid crystal panel known by those skilled in the art at present, uniaxial orientation of polyvinylalcohol is lost by the heat, and hence it is very difficult to provide a state of polarization necessary for stereoscopic imaging.
U.S. Pat. No. 5,537,144 employs a resist material for patterning the polarization layer or a retardation layer. This lowers efficiency in production. U.S. Pat. No. 5,537,144 employs polyvinylalcohol as a material for the polarization layer or the retardation layer. However, as already described, polyvinylalcohol has low heat resistance and it tends to swell when dipped in a solution. Therefore, optical characteristics such as polarization capability, retardation amount and so on are much susceptible to degradation through the steps of sintering, development and so on during patterning of the resist material. Therefore, when a micropolarization plate is fabricated by such a material or through such a method, it is difficult to obtain high-resolution images necessary for stereoscopic display.